Our objective is to characterize the genetic status of subjects enrolled in the longitudinal cohort of the Michigan Alzheimer Disease Research Center (MADRC). We plan to obtain venous blood samples from each subject enrolled in the longitudinal cohort and send it for Apolipoprotein E (ApoE) genotyping. In patients with early-onset familial AD a blood sample will also be sent for presenilin-1 (PS1) genotyping. These data will be shared with the Alzheimer's Disease Data Coordinating Center. In order to analyze our data, we will perform chi-square and logistic regression analyses comparing the frequency of ApoE genotypes of subjects with probable AD and those with non-AD dementias. Similar statistical testing will determine whether PS1 mutations account for a significant portion of early-onset familial AD in patients of different ethnic backgrounds.